#include <iostream>
using namespace std;

namespace ns1{
	int num = 100;
}
namespace ns2{
	int num = 200;
}

//会被编译器放入无名名字空间中
int num = 300;

int main (void)
{
	cout << num << endl;//300
	//using namespace ns1;
	//cout << num << endl;//error

	using namespace ns1;
	using ns2::num;
	cout << num << endl;//200
	cout << ns1::num << endl;//100
	cout << ::num << endl; //300
	return 0;
}
